I'm attempting to port a pathtracer to GLSL, and to do this I need to modify a shader sample program to use a texture as the framebuffer instead of the backbuffer.
This is the vertex fragment
#version 130
out vec2 texCoord;
// https://rauwendaal.net/2014/06/14/rendering-a-screen-covering-triangle-in-opengl/
void main()
{
float x = -1.0 + float((gl_VertexID & 1) << 2);
float y = -1.0 + float((gl_VertexID & 2) << 1);
texCoord.x = x;
texCoord.y = y;
gl_Position = vec4(x, y, 0, 1);
}
This is the setup code
gl.GenFramebuffersEXT(2, _FrameBuffer);
gl.BindFramebufferEXT(OpenGL.GL_FRAMEBUFFER_EXT, _FrameBuffer[0]);
gl.GenRenderbuffersEXT(2, _RaytracerBuffer);
gl.BindRenderbufferEXT(OpenGL.GL_RENDERBUFFER_EXT, _RaytracerBuffer[0]);
gl.RenderbufferStorageEXT(OpenGL.GL_RENDERBUFFER_EXT, OpenGL.GL_RGBA32F, (int)viewport[2], (int)viewport[3]);
And this is the runtime code
// Get a reference to the raytracer shader.
var shader = shaderRayMarch;
// setup first framebuffer (RGB32F)
gl.BindFramebufferEXT(OpenGL.GL_FRAMEBUFFER_EXT, _FrameBuffer[0]);
gl.Viewport((int)viewport[0], (int)viewport[1], (int)viewport[2], (int)viewport[3]); //0,0,width,height)
gl.FramebufferRenderbufferEXT(OpenGL.GL_FRAMEBUFFER_EXT, OpenGL.GL_COLOR_ATTACHMENT0_EXT, OpenGL.GL_RENDERBUFFER_EXT, _RaytracerBuffer[0]);
gl.FramebufferRenderbufferEXT(OpenGL.GL_FRAMEBUFFER_EXT, OpenGL.GL_DEPTH_ATTACHMENT_EXT, OpenGL.GL_RENDERBUFFER_EXT, 0);
uint [] DrawBuffers = new uint[1];
DrawBuffers[0] = OpenGL.GL_COLOR_ATTACHMENT0_EXT;
gl.DrawBuffers(1, DrawBuffers);
shader.Bind(gl);
shader.SetUniform1(gl, "screenWidth", viewport[2]);
shader.SetUniform1(gl, "screenHeight", viewport[3]);
shader.SetUniform1(gl, "fov", 40.0f);
gl.DrawArrays(OpenGL.GL_TRIANGLES, 0, 3);
shader.Unbind(gl);
int[] pixels = new int[(int)viewport[2]*(int)viewport[3]*4];
gl.GetTexImage(_RaytracerBuffer[0], 0, OpenGL.GL_RGBA32F, OpenGL.GL_INT, pixels);
But when I inspect the pixels coming back from GetTexImage they're black. When I bind this texture in a further transfer shader they remain black. I suspect I'm missing something in the setup code for the renderbuffer and would appreciate any suggestions you have!
Renderbuffers are not textures. So when you do glGetTexImage on your renderbuffer, you probably got an OpenGL error. When you tried to bind it as a texture with glBindTexture, you probably got an OpenGL error.
If you want to render to a texture, you should render to a texture. As in glGenTextures/glTexImage2D/glFramebufferTexture2D.
Also, please stop using EXT_framebuffer_object. You should be using the core FBO feature, which requires no "EXT" suffixes. Not unless you're using a really ancient OpenGL version.